The present invention relates to a vehicle brake device, and more particularly to the technique for a brake assist control and an automatic brake control in case of emergency of the vehicle.
When perceiving a danger of a vehicle collision, a driver of a vehicle depresses in haste the brake pedal to decelerate the vehicle. In this case, a maximum braking force is required as a matter of course. Actually, the driver frequently fails to sufficiently depress the brake pedal, however. The result is an insufficient deceleration of the vehicle. To cope with this, there is proposed a vehicle brake device incorporating a brake assist control function thereinto (Japanese Patent Publication Nos. Hei-7-329766 and 8-295224). In the event of emergency, the brake assist control functions to adjust a hydraulic braking pressure so as to maximize a braking force, while compensating for an insufficient braking force applied by the driver.
A conventional vehicle brake device, which is disclosed in Japanese Patent publications referred to above, is shown in FIG. 13.
In the figure, reference numeral 101 is a brake pedal of a vehicle; 102 is a braking-operation detecting circuit for detecting a braking operation made by a driver; 103 is a braking-condition determining circuit for determining as to whether the braking operation is a normal braking operation or an emergency braking operation on the basis of the braking operation detected by the braking-operation detecting circuit 102; and 104 is a braking-force control circuit for controlling a braking force depending on the determination made by the braking-condition determining circuit 103 and applying the so controlled braking force to the vehicle wheels 105.
The operation of the FIG. 13 vehicle brake device is flow charted in FIG. 14.
The vehicle brake device detects a braking operation given when a driver depresses the brake pedal (S101). The vehicle brake device determines whether the braking operation detected is a normal braking operation or an emergency braking operation (S102). A methodological example of the braking-operation determining gains a maximum amount of the braking operation by the driver; it checks if the maximum amount of the braking operation exceeds a predetermined one; if the answer is yes, it determines that the current braking operation is an emergency braking operation. Another example measures a time elapsing from the start of the braking operation till the braking operation reaches its maximum amount; when the elapsing time is within a predetermined predetermined one, it determines that the braking operation is an emergency braking operation.
If the current braking operation is a normal braking operation (S102), the vehicle brake device applies a normal braking force, which is based on the amount of the braking operation by the driver, to the wheels (S103). If it is an emergency braking operation, the vehicle brake device applies a braking force, which is larger than the normal braking force, to the wheels (S104).
As described above, the conventional vehicle brake device judges if the braking operation by the driver is a normal braking operation or an emergency braking operation, on the basis of the amount of the braking operation or the braking operation speed. Therefore, the brake assist control (operates in emergency) in the brake control by the vehicle brake device does not function till the amount of the braking operation by the driver exceeds a predetermined one.
For this reason, in emergency the brake assist control does not function or much time is taken from the start of the braking operation by the driver till the brake assist control starts to operate, for the braking operations by some types of drivers, e.g., woman drivers, who tend to depress the brake pedal not strongly, generally.
For those drivers having the habit of strongly depressing the brake pedal, the brake assist control operates not in emergency, giving the drivers an unnatural drive feeling.